This study is being done to test the effects of doxycycline on inflammation and the bacteria in the body in people with HIV and in people on HIV pre-exposure prophylaxis. This drug is approved by the Food and Drug Administration (FDA) for the treatment of bacterial infections.

The study team will investigate whether the drug has additional effects on inflammation or on the bacteria that live in the body.

This project aims to determine the potential anti-inflammatory and microbiome effects of doxycycline when used as post-exposure prophylaxis (Doxy PEP) for sexually transmitted infections (STIs).

This study is important in the field of research because it allows the investigators to define the systemic and gut anti-inflammatory, microbiome, and resistome effects of doxycycline when used as post-exposure prophylaxis (Doxy PEP) for sexually transmitted infections. The study population that this study seeks to enroll consists of healthy people assigned male at birth, with and without HIV, who are willing to undergo study procedures.

Study procedures will include the collection of medical history, as well as biological specimen sampling, such as blood and rectal tissue biopsies.

The duration of this clinical trial for study participants will be approximately 12 weeks. This will include five in-person visits lasting about 45 minutes to 1 hour (including two biopsy visits).

This study will utilize data specimen banking for future research.

Inclusion Criteria:

• Age >18 years
• Assigned male sex at birth
• Good general health as assessed by a clinician at the screening study visit
• For people with HIV, on suppressive antiretroviral therapy for at least 6 months with the most recent viral load documented <50 copies/ml and the most recent cluster of differentiation 4 (CD4)>300cells/ul
• For people without HIV, taking oral daily, oral on-demand, or injectable pre-exposure prophylaxis for at least 3 months at the time of enrollment, with plans to continue for the duration of the study
• Additional criteria apply

Exclusion Criteria:

• Severe/uncontrolled comorbidities that could influence immune outcomes (e.g., diabetes, hypertension, co-infections), as assessed by the investigator.

• History of inflammatory bowel disease (IBD) or other inflammatory, infiltrative, infectious, or vascular condition involving the lower GI tract that, in the judgment of the investigators, may be worsened by study procedures or may significantly distort the anatomy of the distal large bowel.

• Known allergy to doxycycline

• Use of any antibiotics within 3 months before screening

• Significant lab abnormalities at baseline visit for rectal biopsies,

• Continued need for the following medications during the study:

  1. Aspirin
  2. Warfarin, heparin (LMW or unfractionated), platelet aggregation inhibitors, or fibrinolytic agents
  3. Any form of rectally administered agent besides products (lubricants or douching) used for sexual intercourse
  4. NSAIDS within 72 hours of rectal sampling procedures

• Continued need for, or use during the 90 days before enrollment, of the following medications:

  1. Systemic immunomodulatory agents
  2. Supraphysiologic doses of corticosteroids, except for short-course corticosteroids <7 days duration at the discretion of the investigator. (Gender affirming hormone therapy is not exclusionary.)
  3. Use of experimental medications, vaccines, or biologicals in the 12 months before enrollment

Individual participant data that underlie the results published for this study will be made available for sharing after de-identification.

The research team will share de-identified participant data after publication of the primary results manuscript, anticipated on September 15, 2030. Data will be available indefinitely.

Interested investigators may request de-identified data for secondary analyses and/or meta-analyses by contacting Dr. Kelley via email and completing a data use agreement (DUA) with Emory University.